From 7de83a3c8f11571d5ac4821541e5df1f84f38b70 Mon Sep 17 00:00:00 2001
From: Zhang Jian <zjsariel@gmail.com>
Date: Wed, 12 Sep 2018 20:29:50 +0800
Subject: [PATCH] plan: use the inferred type as the column type in the schema
 (#7624)

---
 executor/aggregate_test.go         | 11 +++++++++++
 plan/logical_plan_builder.go       |  4 +++-
 plan/rule_aggregation_push_down.go |  4 +++-
 plan/rule_decorrelate.go           | 11 +++++++++--
 4 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/executor/aggregate_test.go b/executor/aggregate_test.go
index 3ce424ca18106..0ef14aefa4d39 100644
--- a/executor/aggregate_test.go
+++ b/executor/aggregate_test.go
@@ -602,3 +602,14 @@ func (s *testSuite) TestBuildProjBelowAgg(c *C) {
 		"3 3 15 6,6,6 7",
 		"4 3 18 7,7,7 8"))
 }
+
+func (s *testSuite) TestFirstRowEnum(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec(`use test;`)
+	tk.MustExec(`drop table if exists t;`)
+	tk.MustExec(`create table t(a enum('a', 'b'));`)
+	tk.MustExec(`insert into t values('a');`)
+	tk.MustQuery(`select a from t group by a;`).Check(testkit.Rows(
+		`a`,
+	))
+}
diff --git a/plan/logical_plan_builder.go b/plan/logical_plan_builder.go
index 1d1711fd331ed..bb1888d6c85be 100644
--- a/plan/logical_plan_builder.go
+++ b/plan/logical_plan_builder.go
@@ -115,7 +115,9 @@ func (b *planBuilder) buildAggregation(p LogicalPlan, aggFuncList []*ast.Aggrega
 	for _, col := range p.Schema().Columns {
 		newFunc := aggregation.NewAggFuncDesc(b.ctx, ast.AggFuncFirstRow, []expression.Expression{col}, false)
 		plan4Agg.AggFuncs = append(plan4Agg.AggFuncs, newFunc)
-		schema4Agg.Append(col)
+		newCol, _ := col.Clone().(*expression.Column)
+		newCol.RetType = newFunc.RetTp
+		schema4Agg.Append(newCol)
 	}
 	plan4Agg.SetChildren(p)
 	plan4Agg.GroupByItems = gbyItems
diff --git a/plan/rule_aggregation_push_down.go b/plan/rule_aggregation_push_down.go
index 3089f1d5c9cfd..0cd8d2c0fbc94 100644
--- a/plan/rule_aggregation_push_down.go
+++ b/plan/rule_aggregation_push_down.go
@@ -257,8 +257,10 @@ func (a *aggregationOptimizer) makeNewAgg(ctx sessionctx.Context, aggFuncs []*ag
 	}
 	for _, gbyCol := range gbyCols {
 		firstRow := aggregation.NewAggFuncDesc(agg.ctx, ast.AggFuncFirstRow, []expression.Expression{gbyCol}, false)
+		newCol, _ := gbyCol.Clone().(*expression.Column)
+		newCol.RetType = firstRow.RetTp
 		newAggFuncDescs = append(newAggFuncDescs, firstRow)
-		schema.Append(gbyCol)
+		schema.Append(newCol)
 	}
 	agg.AggFuncs = newAggFuncDescs
 	agg.SetSchema(schema)
diff --git a/plan/rule_decorrelate.go b/plan/rule_decorrelate.go
index 9ea443146a67f..70dedc22d5d08 100644
--- a/plan/rule_decorrelate.go
+++ b/plan/rule_decorrelate.go
@@ -182,13 +182,19 @@ func (s *decorrelateSolver) optimize(p LogicalPlan) (LogicalPlan, error) {
 				agg.SetSchema(apply.Schema())
 				agg.GroupByItems = expression.Column2Exprs(outerPlan.Schema().Keys[0])
 				newAggFuncs := make([]*aggregation.AggFuncDesc, 0, apply.Schema().Len())
-				for _, col := range outerPlan.Schema().Columns {
+
+				outerColsInSchema := make([]*expression.Column, 0, outerPlan.Schema().Len())
+				for i, col := range outerPlan.Schema().Columns {
 					first := aggregation.NewAggFuncDesc(agg.ctx, ast.AggFuncFirstRow, []expression.Expression{col}, false)
 					newAggFuncs = append(newAggFuncs, first)
+
+					outerCol, _ := outerPlan.Schema().Columns[i].Clone().(*expression.Column)
+					outerCol.RetType = first.RetTp
+					outerColsInSchema = append(outerColsInSchema, outerCol)
 				}
 				newAggFuncs = append(newAggFuncs, agg.AggFuncs...)
 				agg.AggFuncs = newAggFuncs
-				apply.SetSchema(expression.MergeSchema(outerPlan.Schema(), innerPlan.Schema()))
+				apply.SetSchema(expression.MergeSchema(expression.NewSchema(outerColsInSchema...), innerPlan.Schema()))
 				np, err := s.optimize(p)
 				if err != nil {
 					return nil, errors.Trace(err)
@@ -229,6 +235,7 @@ func (s *decorrelateSolver) optimize(p LogicalPlan) (LogicalPlan, error) {
 								newFunc := aggregation.NewAggFuncDesc(apply.ctx, ast.AggFuncFirstRow, []expression.Expression{clonedCol}, false)
 								agg.AggFuncs = append(agg.AggFuncs, newFunc)
 								agg.schema.Append(clonedCol.(*expression.Column))
+								agg.schema.Columns[agg.schema.Len()-1].RetType = newFunc.RetTp
 							}
 							// If group by cols don't contain the join key, add it into this.
 							if agg.getGbyColIndex(eqCond.GetArgs()[1].(*expression.Column)) == -1 {